RAPIDITY OF ABSORPTION. 297 



it would be found that the former was always greater than the 

 latter. And so with other substances ; it almost always hap- 

 pens, that if the two liquids placed on opposite sides of a mem- 

 brane be of different densities or specific gravities, a larger 

 quantity of the less dense fluid passes into the more dense, than 

 of the latter into the former. 



The rapidity with which matters may be absorbed from the 

 stomach probably by the bloodvessels chiefly, and diffused 

 through the textures of the body, may be gathered from the 

 history of some experiments by Dr. Bence Jones. From these 

 it appears that even in a quarter of an hour, after being given 

 on an empty stomach, chloride of lithium maybe diffused into 

 all the vascular textures of the body, and into some of the non- 

 vascular, as the cartilage of the hip-joint, as well as into the 

 aqueous humor of the eye. Into the outer part of the crystal- 

 line lens it may pass after a time, varying from half an hour 

 to an hour and a half. Carbonate of lithia, when taken in 

 five or ten-grain doses on an empty stomach, may be detected 

 in the urine in 5 or 10 minutes; or, if the stomach be full at 

 the time of taking the dose, in 20 minutes. It may sometimes 

 be detected in the urine, moreover, for six, seven, or even 

 eight days. 



Some experiments on the absorption of various mineral and 

 vegetable poisons, by Mr. Savory, have brought to light the 

 singular fact, that, in some cases, absorption takes place more 

 rapidly from the rectum than from the stomach. Strychnia, 

 for example, when in solution, produces its poisonous effects 

 much more speedily when introduced into the rectum than 

 into the stomach. When introduced in the solid form, how- 

 ever, it is absorbed more rapidly from the stomach than from 

 the rectum, doubtless because of the greater solvent property 

 of the secretion of the former than of that of the latter. 



With regard to the degree of absorption by living blood- 

 vessels, much depends on the facility with which the substance 

 to be absorbed can penetrate the membrane or tissue which 

 lies between it and the bloodvessels ; for, naturally, the blood- 

 vessels are not bare to absorb. Thus absorption will hardly 

 take place through the epidermis, but is quick when the epi- 

 dermis is removed, and the same vessels are covered with only 

 the surface of the cutis, or with granulations. In general, the 

 absorption through membranes is in an inverse proportion to 

 the thickness of their epithelia ; so Miiller found the urinary 

 bladder of a frog traversed in less than a second ; and the ab- 

 sorption of poisons by the stomach or lungs appears sometimes 

 accomplished in an immeasurably small time. 



The substance to be absorbed must, as a general rule, be in 



